Mobile pipe and rod handling units generally incorporate inclined telescoping masts to limit the weight and dimensions of a unit and to provide for its transportability and for the complicated routine of positioning the unit at the wellhead or the mouth of a borehole. The use of known technical solutions in such handling units applies some additional requirements as regards both the design of the components of the units and the procedure of conducting running and pulling operations.
A topical issue in the drilling of boreholes and servicing of wells is enhancing labor productivity, cutting the time of pipe- and rod-pulling/running operations, and of mounting and dismantling of the unit at a borehole or well. The major possibility for significantly cutting the time of running/pulling operations is offered by overlapping the operations of pipe- or rod-running/pulling and the operations of their coupling/uncoupling and handling. The known units with overlapping of these operations are intended practically exclusively for the drilling of boreholes, and are incorporable only in stationary drilling rigs, as their use in mobile handling units with an inclined mast is prohibited for a number of reasons: they are too heavy and bulky, and their complicated structure involves considerable input of both time and effort for the mounting/dismantling and adjustments of the unit.
There is known a drilling rig (U.S. Pat. No. 3929235) incorporating a system for mechanization of pulling and running operations. The rig comprises a stationary derrick, crown pulley, travelling block with a pipe elevator, and a deflecting system with guides for deflecting the travelling block and the pipe elevator. The overlapping of the operations of running or pulling the drill pipes and the operations of their coupling and uncoupling is made possible owing to the incorporation of the system for lateral deflection of the travelling (tackle) block and elevator from the vertical axis of the borehole. The coaxial alignment of the travelling block and elevator with the borehole is provided for by rigid rail-type guideways mounted internally of the derrick parallel with the axis of the borehole and rigidly secured throughout their length from the crown pulley to the drilling platform. The existence of the two separate deflecting systems with their own drives, with power supply members movable through the entire height of the derrick, and with the necessity of controlling these systems, to say nothing of the relatively great weight and size of the guides and guideways, significantly steps up the weight of the entire unit and complicates its structure and operation. For these reasons, the known structure is illsuited for mobile handling units.
There is further known an apparatus (U.S. Pat. No. 2946464) for handling stands of drill pipes in the drilling of boreholes. The apparatus comprises a stationary derrick, a crown pulley, a split travelling or tackle block with a pipe elevator, a system of flexible guides (cables) for the travelling block and elevator, a platform for accommodating racked pipes and a turntable. Each flexible guide or cable is accommodated within the derrick and has its lower end fast with the platform and its upper end secured to the crown pulley through a power cylinder. For lifting and lowering the travelling block with the main elevator axially of the borehole, and for deflecting the elevator when the operations of running/pulling are made to overlap the operations of coupling/uncoupling, the system of flexible guides or cables is associated with the guide pulleys and trolleys of the travelling block, and of the main and transfer elevators. When the flexible guides or cables are tightened by operating the power cylinder, the main elevator is deflected from a pipe stand, and when the flexible guides or cables are released, the elevator turns, approaches a pipe stand and engages it.
In this apparatus of the prior art, partial overlapping of the running/pulling and coupling/uncoupling operations is attained. After a pipe stand is pulled from the borehole to a successive tool joint, the pipe string is supported by the turntable, while the travelling block with the elevator is run down the pipe to the level of the racking platform. Upon the elevator having engaged the lifted pipe under the joint, the flexible guides or cables of the travelling block are tightened, and the elevator is deflected from the pipe stand. With the above operations performed, the travelling block is run down the pipe, and the lifted pipe stand is uncoupled. With this operation also completed, the uncoupled pipe stand is lifted from the joint and racked. In re-running the stands of drill pipe into the borehole, the operations are reversed.
Hence, the apparatus of the prior art would not provide for complete superposition of the operations of running/pulling drill pipes with the operations of their coupling/uncoupling and moving into and out of the rack. When the travelling block is either lifted or lowered with the empty elevator, it is stopped, the upper end of a stand of drill pipe is re-engaged, the elevator is opened and closed, and the slips are applied and withdrawn, which takes considerable time and adversely affects the efficiency and productivity, while the complicated character of controlling the flexible guide (cable) system, the slips and the transfer elevator, and also of mounting/dismantling the apparatus at the mouth of a borehole practically prohibits the use of this known apparatus in mobile handling units which are supposed to be mounted/dismantled in relatively short periods, and their complexity of control should be minimized.
There is further known an installation for mechanization and in-part automation of pulling and running operations in the drilling of boreholes (U.S. Pat. Nos. 574517, 588340). The installation comprises a stationary derrick, a crown pulley, a split travelling (tackle) block with an elevator, and a centralizer with guides.
The overlapping of the operations is attained owing to the incorporation of the split travelling block with the closed automatic elevator rigidly suspended therefrom, which provides for lifting or lowering block with the elevator axially of the borehole without any additional operations, while passing therethrough either the drill pipe string or an uncoupled length of drill pipe. The upper end of the length of pipe or pipe stand during coupling/uncoupling is held by the centralizer which is supported by the brackets of the derrick for vertical reciprocation along flexible guides (cables) secured between the crown pulley and the bracket of the derrick strictly vertically, axially of the borehole. In this installation, the movement of the travelling block is effected with practically no interruptions, which significantly enhances the efficiency. This is attained, however, only when the centralizer and the rising path of the travelling block are completely axially aligned, as any disturbance of this strict co-axiality incurs the slower-down rate of the running/pulling operations and might even lead to emergencies.
As the travelling block is lifted either with the loaded elevator in pulling a pipe stand from the borehole, or with the empty elevator when the pipe string is run into the borehole, the housing of the rising travelling block at the height of the centralizer engages the latter's cone, whereafter they rise together. As the travelling block is susceptible to a certain degree of swinging in heavy winds, to say nothing of the eventual swinging of semisubmersed handling units of offshore installations, the path of the rising travelling block may become displaced from the axis of the borehole and of the centralizer.
In case of mobile handling units with an inclined mast, the disturbed axial alignment of the travelling block and centralizer can be caused by resilient deformation of the mast loaded by the pipe string. As the load is applied to the travelling block, the load is transmitted via the cable runs of the tackle to the crown pulley, displacing the latter laterally from the axis of the borehole in the mast inclination direction, thus altering the path of the movement of the travelling block from the mouth of the borehole towards the crown pulley. With the ends of the guides of the centralizer being fast with the brackets of the mast and rigidly secured under the crown pulley, and with the centralizer engaging the guides through the carriages for trolleys, the respective axes become displaced, and as the rising travelling block engages the centralizer, the former lifts the latter at the point of inflection of their intended path. The massive centralizer thus develops a tilting which is transmitted to the flexible guides, so that the centralizer could be eventually slanted and jammed. This interrups the operating sequence and may result in an emergency situation.
It can be seen that the last-described design of the prior art is suitable for conducting running and pulling operations exclusively in stationary drillig rigs. It is ill-suited for mobile handling units on account of the eventually disturbed axial alignment of the borehole, centralizer and path of the movement of the travelling block, variable in dependence on the weight of the pipe string. Should the above-described known technical solutions be implemented in mobile handling units, the efficiency would be drastically impaired. Furthermore, the flexible guides of the centralizer perform exclusively the guiding function, as the entire load of the centralizer being halted in its descent is taken up by the brackets of the derrick or mast. Indeed, in the course of running or pulling operations, as the travelling block runs down from its topmost position, the centralizer repeatedly sets itself upon the brackets of the derrick, and when the centralizer engages the bracket, it has the velocity and acceleration equalling the velocity and acceleration of the travelling block descending under the weight of the pipe string. This results in a dynamic impact with the load taken up by the bracket being many times as great as the weight of the centralizer, and this impact load is recurrent.
In a stationary drilling rig there are many ways of enhancing the strength and rigidity of the support brackets at the price of increasing the weight of the derrick and of the entire installation.
In mobile handling units, this capability is severely limited on account of the mass and rigidity of the mast being incomparably lower than in stationary rigs with their derricks.
Thus, the employment of the last-described structure of the prior art in mobile handling units is prohibited by the design of the guides of the centralizer, the increased mass and dimensions of the guides and their associated support members, the prolonged time of running and pulling operations. The use of this structure in mobile handling units is also irrational in view of eventual considerable downtime in well servicing, to say nothing of the time of mitigating eventual emergencies.
There is yet another known unit for handling operations at a borehole or well (U.S. Pat. No. 945630), comprising an inclined mast carrying a racking platform having a central opening at the side of the mast. The top part of the mast has secured thereto a crown pulley connected through hoist line cables to a split travelling (tackle) block, with an elevator suspended from the travelling block. The racking platform is adapted to support a centralizer with carriages for vertical reciprocation along guides in cooperation with the travelling block.
As the pipe string is pulled from the borehole, the elevator on the travelling block lifts the string, the travelling block rising to the level of the centralizer and engaging it, whereafter they continue rising jointly along the guides. The guides are flexible, secured between the racking platform and the crown pulley. With a threaded pipe joint of the string having emerged from the borehole, the movement of the travelling block is halted, the string is held at the mouth of the borehole, and the travelling block with the elevator is run down the pipe stand, with the pulled pipe being simultaneously uncoupled. As the travelling block descends to the level of the racking platform where the lowermost ends of the guides are secured, the centralizer sets itself on the platform, while the travelling block continues to descen. With the lifted pipe stand finally uncoupled, it is drawn laterally away from the travelling block and transferred onto the underpipe block, and the travelling block is raised with the successive engaged pipe stand.
With no load applied to the travelling block, the respective vertical axes of the crown pulley, travelling block and centralizer are aligned with the axis of the borehole, and the probability of matching engagement of the rising travelling block with the centralizer is fairly high. However, with the pipe string being pulled this co-axial alignment is disturbed. This is caused by the weight of the string in units of the described type being transmitted as a load through the hoist line cables to the mast. On account of definite flexibility of the mast, this causes an increase of the latter's angle of inclination, whereby the crown block is displaced laterally in the direction of inclination of the mast, the value of the angle of inclination in this case not being permanent, but depending on the load, i.e. on the length of the string being pulled. Consequently, as the pipe string is pulled, the crown pulley becomes offset from the borehole axis in the direction of the inclination of the mast, whereas the guides rigidly secured to the racking platform would not let the centralizer move in the direction of the displacement of the crown pulley in a horizontal plane. The displacement of the crown pulley leads to a changed path of rising of the travelling block and disturbed axial alignment of the travelling block and centralizer. As the travelling block is moved upwardly from the mouth of the borehole towards the crown pulley, it approaches the centralizer on the racking platform, and to ensure its matching engagement with the centralizer, the speed of the rising travelling block has to be slowed down to preclude an emergency situation. The matching engagement can be ensured by forced centering of the travelling block, i.e. by forced adjustment of the natural rising path of the travelling block from the borehole mouth to the crown pulley. However, the forced displacement of the travelling block disturbs the normal procedure of pulling operations, which incurs a substantial loss of time. In this way the efficiency of the handling unit is severely impaired.
Furthermore, in the descent of the travelling block with the centralizer, the setting of the centralizer on its stops on the racking platform involves recurrent dynamic impacts. As the descending centralizer engages the stops, it has a speed equalling the speed of the travelling block descending under the weight of the pipe string. Thus, at the moment of the setting of the centralizer onto its stops on the racking platform, the load caused by the moving weight of the centralizer is many times as great as the static load. Thus, each such setting is accompanied by violent vibration of the platform and of the entire mast structure, and the derrick man on the fourble board is made incapable of performing his functions.
Hence, the employment of the last-described known structure in mobile handling units is not practically feasible, as it prolongs the time of running and pulling operations, leads eventually to emergency situations, disturbs the normal operating procedure, and ultimately brings down the efficiency of the unit.